Some completion methods require sequential isolation of adjacent zones in an interval to perform treatments such as fracing. Typically the zones are isolated with packers and in between them there are sliding sleeves that can be selectively opened to provide access. Typically, this assembly is run in to position, and then a ball or plug is pumped down to the bottom which closes off the flow path through the bottom end of the liner. Pressure is applied and the packers are set, creating multiple isolated zones. The tubular string is pressurized and the lowermost sliding sleeve is opened. After the lowermost zone is treated a ball is dropped on a lowermost seat to close off the zone just treated and the pressure is built up on this first dropped ball to open the next sliding sleeve up. After that treatment an even bigger ball lands on an even bigger seat to close off the second zone just treated. The process is repeated until all zones are treated using a progression of bigger and bigger seats as the treatment moves toward the surface. At the end, the balls on all the seats are either floated to the surface when the flow commences from the treated formation or the assembly of all the seats and the balls that are respectively on them are milled out so as not to impede subsequent production from the treated zone. This technique is shown in U.S. Pat. No. 6,907,936. The problem with it is that different sized seats are required at specific locations to make the isolation system work and in the end there are some rather small passages through the smallest of the seats even if the balls are floated out that then requires a discrete step of milling out the seat and ball near all but one sliding sleeve.
Techniques have been developed to temporarily block wellbores using dissolving or other wise disappearing plugs. Such devices are illustrated in U.S. Pat. Nos. 6,220,350, 6,712,153 and 6,896,063. Some packers are built to be disposable involving the use of degradable polymers as illustrated in US Publication No. 2005/0205264; 2005/0205265 and 2005/0205266. Some assemblies involve landing collars that can be changed from a go to a no go orientation with a shifting tool that also doubles as a tool to operate sliding sleeves. This is illustrated in US Publication No. 2004/0238173. Yet other designs that create selective access into a formation by using perforating charges that blow out plugs in casing or pressure actuated pistons with internal rupture discs are illustrated in U.S. Pat. Nos. 5,660,232 and 5,425,424. U.S. Pat. No. 6,769,491 illustrates a typical anchor assembly for a downhole tool.
The present invention seeks to streamline certain downhole operations by matching profiles on plugs to those on sliding sleeves or nipple profiles. This allows a specific plug to be located at a certain location and bypass other potential landing locations. The flow path can be identical in size for the duration of the zone and yet different portions can be addressed in a particular sequence. Apart from that, the plugs, after having served their purpose, reopen the flow path for further operations. These and other benefits of the present invention will be more readily understood by those skilled in the art from a review of the description of the preferred embodiment that appears below, as well as the drawings and the claims, which define the full scope of the invention.